Abstract

A hybrid plasmonic waveguide with double low-index nano-slots is introduced. The fabrication is simple and compatible with the standard processes for SOI wafers. The theoretical investigation shows that the present hybrid plasmonic waveguide has a low loss and consequently a relatively long propagation distance (at the order of several tens of λ). For TE polarization, there is a strong field enhancement in the double nano-slots. More power is confined in the low-index nano-slots for a smaller core width. For a 50nm-wide hybrid plasmonic waveguide with double 10nm-wide slots, the power confinement factor in the nano-slots is as high as 85% and the effective area is as small as 0.007μm2 at 1550nm. Consequently, the power density in the nano-slots becomes very high, e.g., >120μm–2, which is very desired for many applications. For the present hybrid plasmonic waveguide, the lateral dimension could be less than 50nm and the calculated decoupled separation for two parallel identical waveguides is only 0.62μm, which is helpful to realize photonic integration circuits with ultra-high integration density.

The calculated field distribution for the major component Ex(x,y) of the quasi-TE fundamental mode of the present hybrid plasmonic waveguide with wco = 50nm and wSiO2 = 10nm. Here the field distributions Ex(x0, y) and Ex(x, y0) are also shown. It can be seen that the optical field at the 10nm-SiO2 nano-slots is enhanced greatly.

For the cases of wslot = 10nm, 20nm, 30nm, and 50nm, (a) the real part of the effective index of the quasi-TE fundamental mode; (b) the power confinement factor in the low-index slots PSiO2; (c) the power confinement factor in the Si rib PSi; (d) the normalized power density; (e) the effective areas Aeff; (f) the propagation distance Lprop. Here we choose a relatively thick SiO2 up-cladding hSiO2 = 300nm and hSi = 340nm.

(a) The cross section for a coupling system with two parallel identical hybrid plasmonic waveguides; (b) the calculated coupling length Lc as the waveguide core width wco varies for different separations s between the two waveguides (s = 200, 300, 400, 500, 600, 700, and 800nm); (c) the calculated coupling length Lc as the separation s increases for a fixed core width wco = 50nm; The decoupled separation sdc is as small as 620nm.